This invention relates to ceramics and more particularly to mullite.
Conventional techniques for preparation of fibrous ceramic thermal insulators and fibrous ceramic preforms for ceramic/metal matrix composites are pressing and vacuum forming g with the additions of organic or inorganic binders. Both techniques require deagglomerating the fibers and mixing with the binders before forming and then drying, machining, removing binder and prefiring (if necessary) after forming. For example, U.S. Pat. No. 3,104,943 entitled "Spinnable Mullite Fibers and their Preparation" which was issued to Kenneth L. Berry on Apr. 25, 1960, discloses a method whereby mullite fibers are crystallized from a vapor phase derived from heating sources of Si, Al, O.sub.2, and S in a atmosphere containing at least one percent H.sub.2 at 800.degree.-1200.degree. C. A suspension of the such prepared fibers is than filtrated to form a felt. This step requires extra handling which increases the cost and may damage the fibers. Additionally, the complexity of the felt or mat shapes is limited by the filtration technique. Moreover, the resulting felt is composed of polycrystalline fibers rather than single crystal whiskers. As a reinforcing material, whiskers are preferable to fibers because they are single crystals and their properties are not affected by grain growth and grain boundary-induced creep at high temperatures. The low free energy and high modulus and strength of whiskers compared to polycrystalline materials make it possible to use whiskers to reinforce matrices of the same composition.
Therefore, it would be desirable to provide a simple, economical and in-situ process capable of producing high-quality single crystal mullite-whisker felt even in complex shapes with good dimensional control.